5
CHANGING THE TONE OF YOUR COMBO
If you are the type of person who likes modifying gear, then you may be interested in experimenting
with changing some things about your combo. One of the easiest tone mods you could perform on your
cab is to change the speaker. We have chosen this Jensen speaker because of its response and tonal
qualities when driven by the Percolator. However, tone is mostly a matter of preference and taste, so
there could be an endless number of different 8” speakers that could be used depending on what you
like. We encourage you to try them out (see the section called “REPLACING THE SPEAKER”). Find one
that works well for the type of music you want to play.
Another mod is to experiment with different port sizes. This cab is mostly open-back, which gives some
nice dimensional presence to the sound when playing in a smaller room or if the back of the cab is
near a wall. The sound seems to swirl around as our ears are affected by the phase differences, but
you could add some more ports to make it more closed-back. This takes away from the natural, swirling
sound, but gives a much more punchy, stronger mid-range tonality. This is one of the reasons the classic
Marshall (closed back) sound can cut through a mix so well. You can always mix and match port sizes
too. You could even bore holes in some of them to “port” the box. Between changing the speaker and
playing with the ports, the possibilities are endless! Be creative, experiment and explore!
REPLACING THE TUBE
Tubes are made of several fragile mechanical components closely spaced in a vacuum sealed glass
enclosure. There are several factors affecting the tube’s longevity, which include how hard the tube
is pushed and how often the tube is used. In the case of a tube guitar amplifier, vibration from the
speakers, traveling on the road, and setup and tear down all have a negative effect on the longevity of
the tube. Any time you hear a change in the amp’s performance the tube should be the first thing you
check. If your amplifier loses power, fades in and out, loses dynamic or tonal range, or makes unusual
sounds or excess noise, you should look into replacing the tube.
To remove the tube, gently rock the tube back and forth while slightly lifting. Put a tube into the socket
in just the opposite way. In working with new tubes, first check to make sure all the pins on the tube
are straight (sometimes they come from the factory with slightly bent pins). If any pins are bent very
gently straighten them with some needle nose pliers until the tube fits into the socket. Be patient and
take your time in doing this; you can easily break the glass enclosure if you are not careful!
The tube used in the Percolator is what is known as a “new old stock” item, meaning that they are
still available new, but are no longer being made. This particular tube was last made in the early
1990’s but we maintain ample stock here at the lab. The tube was originally used in tube televisions
but there are very few of those still around! This was one of the main reasons we decided to design
the Percolator around this tube: they are easy to find, but unusual in instrument amplifiers, creating a
unique tone. When the time comes to replace the tube in your amp, we here at Zeppelin Design Labs
would be happy to sell you a replacement, but you can also check the standard NOS tube dealers
around the web, and even places like Ebay. While you are at it, you might want to pick up a backup
tube for the future.
